Shhhh! Pratt Competing To Make Quieter Jet Engines

The latest engine to roll out of Pratt & Whitney just might deliver what the aerospace industry has sought in a commercial jet for more than a century — some peace and quiet.

"The tremendous racket that is at present associated with the aeroplane plays a considerable part in prejudicing the public against these machines," read a 1911 editorial in "The Aero," an industry publication based in London, that advocated the "fitting of silencers" on engines.

Pratt's PurePower geared turbofan engine — known for its efficiency with jet fuel — is also a long stride toward quieter flight. With a noise profile that comes in 20 decibels below the most stringent airport standards, the engine is expected to be noticed by far fewer people on the ground.

And the result: Airlines have ordered more than 3,500 of the engines for new aircraft.

A twin-engine airplane flying 1,000 feet overhead comes in as loud as a noisy dishwasher to people on the ground, about 70 decibels. So living by an airport is like having a reprise of that dishwasher every few minutes throughout the day. Pratt's engine, about 20 decibels lower, will be more like the hum of a refrigerator.

Since those early, loud days of jet flight, the aerospace world has cycled through its share of solutions. Mechanical ideas included putting mufflers on engines, but they proved to be heavy. Others focused on advanced materials that deaden sound. The latest advances have come from relying more on the quieter portions of the engine for thrust.

But with airplanes still considerably loud, airlines are forced to operate within noise budgets set by airports; pay noise fees; and jump through hoops to avoid being especially loud over populated areas. The major engine-makers, Pratt and General Electric, are both releasing engines that they say are significantly quieter than existing technologies.

"This is the first time in commercial aviation that you can't blame the engine guys anymore," said Alan Epstein, Pratt's head of technology. He said it won't be long until "airplanes get to the noise levels of highways."

Analysts say the drop in engine noise — Pratt, a division of United Technologies Corp., advertises a 75 percent reduction — is a jump forward in an industry used to smaller advances. "This is a big change, not just an incremental improvement," said Richard Aboulafia, aerospace analyst with the Teal Group in Fairfax, Va.

The engine — some versions will be assembled in Middletown — lines up against its noise-conscious competitor, GE Aviation's LEAP engine, which bets on the cumulative effect of a handful of material and design changes to reduce noise, Aboulafia said. The Pratt engine, on the other hand, is a more straightforward approach, accomplished by moving more air, slower.

"It doesn't depend on a host of new incremental improvements," he said. "That definitely has its appeal."

For airplane makers, the less noisy engines — combined with more aerodynamic airframes — will give their airline customers some wiggle room within the "noise budgets" at airports, which are set to decrease over time.

A quieter engine "enables them to preserve their existing operations," said Raphael Sheffield, head of technical marketing at Airbus, which will havea version of Pratt's engine on its new A320neo single-aisle airliner.

And beyond that, the quieter engine will give airlines some room to possibly add more flights "within the existing noise budget."

With projections for airlines to see annual increases in passenger miles, airports and the aviation industry are looking at how to expand while remaining good neighbors to residents in surrounding areas. Noise and emissions are expected to be major issues, and Pratt and other engine-makers are competing to offer the least noisy engine.

"The biggest impediment to the expansion of air transportation in the developed world is noise," Epstein said.

A Simpler Solution

The Pratt engine is quieter than other engines, but it is also bigger.

An airplane engine gets its thrust from one of two related sections: the engine core, where the air compression and combustion occur, and the fan, which is driven by the engine core and pushes a large volume of air with large blades.

Part of the air that enters an engine goes through the core, where it's mixed with jet fuel and ignited, but most of the air goes around the core. Over time, engine-makers like Pratt have made smaller and smaller jet cores, while enlarging the size of the fan and its blades to give more thrust with less noise.

"You can have the same amount of thrust with a small amount of air going very fast, or a much larger amount of air slowly," Epstein said. "So more air means the engine needs to get bigger and bigger in diameter."